[OZAPRS] LM7805 and caps

Ian ZL1VFO zl1vfo at yahoo.co.uk
Mon Aug 27 12:16:59 EST 2007

> Message: 4
> From: "Andrew Rich" <vk4tec at people.net.au>
> Subject: [OZAPRS] LM7805 and caps

> Can someone explain to me why this is so:
> I have been building some projects now that use LM7805 voltage
> This is now the second time I have had issues with a PIC chip not
> It is only when I add caps to the input and the output that it settles
> Looking on the CRO, the DC looked noisy.
> I thought that the caps where there to trap AC.
> Do caps on an LM7805 player a larger role ? Is there something inside
> reg that needs external C ?

The little beggers sometimes take off and oscillate without any C
around them.

I usually put 10-100uF & a 0.1uF ceramic across the input to gnd, and
several uF and another 0.1uF ceramic across the output. Might be a bit
of an overkill, but I'd prefer these things didn't take off and cause
wierd effects in uP or other logic circuits...


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